shorewall_code/manpages/shorewall-interfaces.xml
teastep bd9ea3c47f Make the mss interface option clear
Signed-off-by: Tom Eastep <teastep@shorewall.net>

git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@9863 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
2009-04-14 23:25:19 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<refentry>
<refmeta>
<refentrytitle>shorewall-interfaces</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>interfaces</refname>
<refpurpose>Shorewall interfaces file</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>/etc/shorewall/interfaces</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The interfaces file serves to define the firewall's network
interfaces to Shorewall. The order of entries in this file is not
significant in determining zone composition.</para>
<para>The columns in the file are as follows.</para>
<variablelist>
<varlistentry>
<term><emphasis role="bold">ZONE</emphasis> -
<emphasis>zone-name</emphasis></term>
<listitem>
<para>Zone for this interface. Must match the name of a zone
declared in /etc/shorewall/zones. You may not list the firewall zone
in this column.</para>
<para>If the interface serves multiple zones that will be defined in
the <ulink url="shorewall-hosts.html">shorewall-hosts</ulink>(5)
file, you should place "-" in this column.</para>
<para>If there are multiple interfaces to the same zone, you must
list them in separate entries.</para>
<para>Example:</para>
<blockquote>
<programlisting>#ZONE INTERFACE BROADCAST
loc eth1 -
loc eth2 -</programlisting>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">INTERFACE</emphasis> -
<emphasis>interface</emphasis><emphasis
role="bold">[:</emphasis><emphasis>port</emphasis><emphasis
role="bold">]</emphasis></term>
<listitem>
<para>Name of interface. Each interface may be listed only once in
this file. You may NOT specify the name of a "virtual" interface
(e.g., eth0:0) here; see <ulink
url="http://www.shorewall.net/FAQ.htm#faq18">http://www.shorewall.net/FAQ.htm#faq18</ulink></para>
<para>You may use wildcards here by specifying a prefix followed by
the plus sign ("+"). For example, if you want to make an entry that
applies to all PPP interfaces, use 'ppp+'; that would match ppp0,
ppp1, ppp2, …</para>
<para>When using Shorewall versions before 4.1.4, care must be
exercised when using wildcards where there is another zone that uses
a matching specific interface. See <ulink
url="shorewall-nesting.html">shorewall-nesting</ulink>(5) for a
discussion of this problem.</para>
<para>Beginning with Shorewall 4.2.3, Shorewall-perl allows '+' as
an interface name.</para>
<para>There is no need to define the loopback interface (lo) in this
file.</para>
<para>(Shorewall-perl only) If a <replaceable>port</replaceable> is
given, then the <replaceable>interface</replaceable> must have been
defined previously with the <option>bridge</option> option. The
OPTIONS column may not contain the following options when a
<replaceable>port</replaceable> is given.</para>
<simplelist>
<member>arp_filter</member>
<member>arp_ignore</member>
<member>bridge</member>
<member>log_martians</member>
<member>mss</member>
<member>optional</member>
<member>proxyarp</member>
<member>routefilter</member>
<member>sourceroute</member>
<member>upnp</member>
</simplelist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">BROADCAST</emphasis> (Optional) -
{<emphasis role="bold">-</emphasis>|<emphasis
role="bold">detect</emphasis>|<emphasis>address</emphasis>[,<emphasis>address</emphasis>]...}</term>
<listitem>
<para>The broadcast address(es) for the network(s) to which the
interface belongs. For P-T-P interfaces, this column is left blank.
If the interface has multiple addresses on multiple subnets then
list the broadcast addresses as a comma-separated list.</para>
<para>If you use the special value <emphasis
role="bold">detect</emphasis>, Shorewall will detect the broadcast
address(es) for you. If you select this option, the interface must
be up before the firewall is started.</para>
<para>If you don't want to give a value for this column but you want
to enter a value in the OPTIONS column, enter <emphasis
role="bold">-</emphasis> in this column.</para>
<para><emphasis role="bold">Note to Shorewall-perl users:</emphasis>
Shorewall-perl only supports <option>detect</option> or <emphasis
role="bold">-</emphasis> in this column. If you specify
<replaceable>address</replaceable>es, a compilation warning will be
issued.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">OPTIONS</emphasis> (Optional) -
[<emphasis>option</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>option</emphasis>]...]</term>
<listitem>
<para>A comma-separated list of options from the following list. The
order in which you list the options is not significant but the list
should have no embedded white space.</para>
<variablelist>
<varlistentry>
<term><emphasis role="bold">arp_filter[={0|1}]</emphasis></term>
<listitem>
<para>If specified, this interface will only respond to ARP
who-has requests for IP addresses configured on the interface.
If not specified, the interface can respond to ARP who-has
requests for IP addresses on any of the firewall's interface.
The interface must be up when Shorewall is started.</para>
<para>The option value (0 or 1) may only be specified if you
are using Shorewall-perl. With Shorewall-perl, only those
interfaces with the <option>arp_filter</option> option will
have their setting changes; the value assigned to the setting
will be the value specified (if any) or 1 if no value is
given.</para>
<para></para>
<note>
<para>This option does not work with a wild-card
<replaceable>interface</replaceable> name (e.g., eth0.+) in
the INTERFACE column.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">arp_ignore</emphasis>[=<emphasis>number</emphasis>]</term>
<listitem>
<para>If specified, this interface will respond to arp
requests based on the value of <emphasis>number</emphasis>
(defaults to 1).</para>
<para>1 - reply only if the target IP address is local address
configured on the incoming interface</para>
<para>2 - reply only if the target IP address is local address
configured on the incoming interface and the sender's IP
address is part from same subnet on this interface</para>
<para>3 - do not reply for local addresses configured with
scope host, only resolutions for global and link</para>
<para>4-7 - reserved</para>
<para>8 - do not reply for all local addresses</para>
<para></para>
<note>
<para>This option does not work with a wild-card
<replaceable>interface</replaceable> name (e.g., eth0.+) in
the INTERFACE column.</para>
</note>
<para></para>
<warning>
<para>Do not specify <emphasis
role="bold">arp_ignore</emphasis> for any interface involved
in <ulink url="../ProxyARP.htm">Proxy ARP</ulink>.</para>
</warning>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">blacklist</emphasis></term>
<listitem>
<para>Check packets arriving on this interface against the
<ulink
url="shorewall-blacklist.html">shorewall-blacklist</ulink>(5)
file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">bridge</emphasis></term>
<listitem>
<para>(Shorewall-perl only) Designates the interface as a
bridge.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">dhcp</emphasis></term>
<listitem>
<para>Specify this option when any of the following are
true:</para>
<orderedlist spacing="compact">
<listitem>
<para>the interface gets its IP address via DHCP</para>
</listitem>
<listitem>
<para>the interface is used by a DHCP server running on
the firewall</para>
</listitem>
<listitem>
<para>the interface has a static IP but is on a LAN
segment with lots of DHCP clients.</para>
</listitem>
<listitem>
<para>the interface is a <ulink
url="../SimpleBridge.html">simple bridge</ulink> with a
DHCP server on one port and DHCP clients on another
port.</para>
<note>
<para>If you use <ulink
url="../bridge-Shorewall-perl.html">Shorewall-perl for
firewall/bridging</ulink>, then you need to include
DHCP-specific rules in <ulink
url="shorewall-rules.html">shorewall-rules</ulink>(8).
DHCP uses UDP ports 67 and 68.</para>
</note>
</listitem>
</orderedlist>
<para>This option allows DHCP datagrams to enter and leave the
interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">logmartians[={0|1}]</emphasis></term>
<listitem>
<para>Turn on kernel martian logging (logging of packets with
impossible source addresses. It is strongly suggested that if
you set <emphasis role="bold">routefilter</emphasis> on an
interface that you also set <emphasis
role="bold">logmartians</emphasis>. Even if you do not specify
the <option>routefilter</option> option, it is a good idea to
specify <option>logmartians</option> because your distribution
may be enabling route filtering without you knowing it.</para>
<para>The option value (0 or 1) may only be specified if you
are using Shorewall-perl. With Shorewall-perl, only those
interfaces with the <option>logmartians</option> option will
have their setting changes; the value assigned to the setting
will be the value specified (if any) or 1 if no value is
given.</para>
<para>To find out if route filtering is set on a given
<replaceable>interface</replaceable>, check the contents of
<filename>/proc/sys/net/ipv4/conf/<replaceable>interface</replaceable>/rp_filter</filename>
- a non-zero value indicates that route filtering is
enabled.</para>
<para>Example:</para>
<programlisting> teastep@lists:~$ <command>cat /proc/sys/net/ipv4/conf/eth0/rp_filter </command>
1
teastep@lists:~$ </programlisting>
<para></para>
<note>
<para>This option does not work with a wild-card
<replaceable>interface</replaceable> name (e.g., eth0.+) in
the INTERFACE column.</para>
</note>
<blockquote>
<para>This option may also be enabled globally in the <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5)
file.</para>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">maclist</emphasis></term>
<listitem>
<para>Connection requests from this interface are compared
against the contents of <ulink
url="shorewall-maclist.html">shorewall-maclist</ulink>(5). If
this option is specified, the interface must be an ethernet
NIC and must be up before Shorewall is started.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">mss</emphasis>=<emphasis>number</emphasis></term>
<listitem>
<para>Added in Shorewall 4.0.3. Causes forwarded TCP SYN
packets entering or leaving on this interface to have their
MSS field set to the specified
<replaceable>number</replaceable>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">norfc1918</emphasis></term>
<listitem>
<para>This interface should not receive any packets whose
source is in one of the ranges reserved by RFC 1918 (i.e.,
private or "non-routable" addresses). If packet mangling or
connection-tracking match is enabled in your kernel, packets
whose destination addresses are reserved by RFC 1918 are also
rejected.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">nosmurfs</emphasis></term>
<listitem>
<para>Filter packets for smurfs (packets with a broadcast
address as the source).</para>
<para>Smurfs will be optionally logged based on the setting of
SMURF_LOG_LEVEL in <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5). After
logging, the packets are dropped.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">optional</emphasis></term>
<listitem>
<para>Only supported by Shorewall-perl. When
<option>optional</option> is specified for an interface,
Shorewall will be silent when:</para>
<itemizedlist>
<listitem>
<para>a <filename
class="directory">/proc/sys/net/ipv4/conf/</filename>
entry for the interface cannot be modified (including for
proxy ARP).</para>
</listitem>
<listitem>
<para>The first address of the interface cannot be
obtained.</para>
</listitem>
</itemizedlist>
<para></para>
<blockquote>
<para>I specify <option>optional</option> on interfaces to
Xen virtual machines that may or may not be running when
Shorewall is [re]started.</para>
<para></para>
<caution>
<para>Use <option>optional</option> at your own risk. If
you [re]start Shorewall when an 'optional' interface is
not available and then do a <command>shorewall
save</command>, subsequent <command>shorewall
restore</command> and <command>shorewall -f
start</command> operations will instantiate a ruleset that
does not support that interface, even if it is available
at the time of the restore/start.</para>
</caution>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">proxyarp[={0|1}]</emphasis></term>
<listitem>
<para>Sets
/proc/sys/net/ipv4/conf/<emphasis>interface</emphasis>/proxy_arp.
Do NOT use this option if you are employing Proxy ARP through
entries in <ulink
url="shorewall-proxyarp.html">shorewall-proxyarp</ulink>(5).
This option is intended solely for use with Proxy ARP
sub-networking as described at: <ulink
url="http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html">http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html.
</ulink></para>
<para><emphasis role="bold">Note</emphasis>: This option does
not work with a wild-card <replaceable>interface</replaceable>
name (e.g., eth0.+) in the INTERFACE column.</para>
<para>The option value (0 or 1) may only be specified if you
are using Shorewall-perl. With Shorewall-perl, only those
interfaces with the <option>proxyarp</option> option will have
their setting changed; the value assigned to the setting will
be the value specified (if any) or 1 if no value is
given.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">routeback</emphasis></term>
<listitem>
<para>If specified, indicates that Shorewall should include
rules that allow traffic arriving on this interface to be
routed back out that same interface. This option is also
required when you have used a wildcard in the INTERFACE column
if you want to allow traffic between the interfaces that match
the wildcard.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">routefilter[={0|1}]</emphasis></term>
<listitem>
<para>Turn on kernel route filtering for this interface
(anti-spoofing measure).</para>
<para>The option value (0 or 1) may only be specified if you
are using Shorewall-perl. With Shorewall-perl, only those
interfaces with the <option>routefilter</option> option will
have their setting changes; the value assigned to the setting
will be the value specified (if any) or 1 if no value is
given.</para>
<para></para>
<note>
<para>This option does not work with a wild-card
<replaceable>interface</replaceable> name (e.g., eth0.+) in
the INTERFACE column.</para>
</note>
<blockquote>
<para>This option can also be enabled globally in the <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5)
file.</para>
</blockquote>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">sourceroute[={0|1}]</emphasis></term>
<listitem>
<para>If this option is not specified for an interface, then
source-routed packets will not be accepted from that interface
(sets
/proc/sys/net/ipv4/conf/<emphasis>interface</emphasis>/accept_source_route
to 1). Only set this option if you know what you are doing.
This might represent a security risk and is not usually
needed.</para>
<para>The option value (0 or 1) may only be specified if you
are using Shorewall-perl. With Shorewall-perl, only those
interfaces with the <option>sourceroute</option> option will
have their setting changes; the value assigned to the setting
will be the value specified (if any) or 1 if no value is
given.</para>
<para></para>
<note>
<para>This option does not work with a wild-card
<replaceable>interface</replaceable> name (e.g., eth0.+) in
the INTERFACE column.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">tcpflags</emphasis></term>
<listitem>
<para>Packets arriving on this interface are checked for
certain illegal combinations of TCP flags. Packets found to
have such a combination of flags are handled according to the
setting of TCP_FLAGS_DISPOSITION after having been logged
according to the setting of TCP_FLAGS_LOG_LEVEL.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">upnp</emphasis></term>
<listitem>
<para>Incoming requests from this interface may be remapped
via UPNP (upnpd). See <ulink
url="../UPnP.html">http://www.shorewall.net/UPnP.html</ulink>.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Example</title>
<variablelist>
<varlistentry>
<term>Example 1:</term>
<listitem>
<para>Suppose you have eth0 connected to a DSL modem and eth1
connected to your local network and that your local subnet is
192.168.1.0/24. The interface gets it's IP address via DHCP from
subnet 206.191.149.192/27. You have a DMZ with subnet 192.168.2.0/24
using eth2.</para>
<para>Your entries for this setup would look like:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net eth0 206.191.149.223 dhcp
loc eth1 192.168.1.255
dmz eth2 192.168.2.255</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 2:</term>
<listitem>
<para>The same configuration without specifying broadcast addresses
is:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net eth0 detect dhcp
loc eth1 detect
dmz eth2 detect</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 3:</term>
<listitem>
<para>You have a simple dial-in system with no ethernet
connections.</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net ppp0 -</programlisting>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>FILES</title>
<para>/etc/shorewall/interfaces</para>
</refsect1>
<refsect1>
<title>See ALSO</title>
<para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
shorewall-blacklist(5), shorewall-hosts(5), shorewall-ipsec(5),
shorewall-maclist(5), shorewall-masq(5), shorewall-nat(5),
shorewall-netmap(5), shorewall-params(5), shorewall-policy(5),
shorewall-providers(5), shorewall-proxyarp(5), shorewall-route_rules(5),
shorewall-routestopped(5), shorewall-rules(5), shorewall.conf(5),
shorewall-tcclasses(5), shorewall-tcdevices(5), shorewall-tcrules(5),
shorewall-tos(5), shorewall-tunnels(5), shorewall-zones(5)</para>
</refsect1>
</refentry>